Which of the following time spans represent the greatest length of time?

A. Era
B. Eon
C. Period
D. Epoch

my answer is b.

I am inclined to agree, 10^9 years.

Great! You chose option B, which is "Eon." Now, let me explain how you can arrive at this answer.

In the geological timescale, geologists and scientists categorize the Earth's history into multiple divisions based on the length of time. Let's go through each option to understand their respective time spans:

A. Era: An era is a significant division of the geologic timescale. It represents a substantial amount of time, typically lasting for millions to hundreds of millions of years. Eras are further divided into periods.

B. Eon: An eon is the largest time unit in the geological timescale. It encompasses billions of years. The most commonly recognized eons are the "Phanerozoic Eon," which covers the past 541 million years, and the "Precambrian Eon," which spans the time before the Phanerozoic Eon.

C. Period: A period is a division of an era. It represents a relatively shorter span of time than an era, typically lasting for tens of millions to hundreds of millions of years. For example, the Mesozoic Era is divided into periods, including the Triassic, Jurassic, and Cretaceous periods.

D. Epoch: An epoch is a smaller subdivision of a period. It represents an even shorter duration of time, typically lasting for several million years. For instance, the Tertiary period is further divided into epochs, such as the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs.

Based on this understanding, you correctly chose option B, "Eon," as it represents the greatest length of time. Eons encompass billions of years, while eras, periods, and epochs represent progressively shorter intervals of time.